Anti-HIV drugs must target cells of the macrophage lineage because they are one of the first cell types infected and provide a persistent reservoir for HIV replication. It is clear that pretreatment of monocyte- derived macrophages (MDMs) with IFN-a2 and -[unreadable] protects them from HIV replication by inhibiting viral DMA synthesis and RNA production. However, the full repertoire of host factors induced by Type I interferon (IFN) treatment that protect cells from HIV replication is presently unknown. Furthermore, recent clinical trials have shown that pegylated forms of IFN-a2 can reduce viral loads in HIV-infected patients. Following renewed interest for IFN in the clinical setting, it is important to determine the efficacies of different Type I IFNs for HIV inhibition, identify interferon-stimulated genes (ISGs) with anti-HIV properties, and investigate the mechanisms by which they inhibit HIV replication. The first step in anti-HIV ISG discovery is to identify Type I IFNs that are strong inhibitors of HIV replication in MDMs. IFN-a1, -a2, -a7, -[unreadable], -?, -?, and -t4 are representative of the different classes of Type I IFN and their HIV inhibitory properties will be determined by calculating their 50% effective inhibitory concentration (IC50). Gene expression analysis of uninfected MDMs will then be used to identify the subset of ISGs modulated by each Type I IFN under study. Anti-HIV ISGs will initially be identified as genes upregulated in common by Type I IFNs that are strong inhibitors (low IC50) of HIV replication compared to those that are only weakly inhibitory (high IC50). Anti-HIV ISGs will then be prioritized using the literature record and pathway, domain and promoter analysis, and their expression confirmed at the protein level. The stage of the HIV life cycle inhibited by a particular anti-HIV ISG will be determined in gene overexpression experiments by measuring virus replication at the DMA, RNA and protein (p24) level. Gene knockdown experiments will determine the contribution of an anti-HIV ISG to the general IFN response and reveal those that are truly necessary for HIV inhibition. When these studies are complete, we will have determined the therapeutic potential of different species of Type I IFN for the inhibition of HIV replication and identified the specific ISGs that facilitate this inhibition. Lay Abstract. This proposal will identify those species of Type I interferon that are the most effective at inhibiting HIV replication. Furthermore, this research aims to determine those cellular genes whose expression is turned on by interferon treatment and produce proteins that inhibit HIV replication. Knowledge of genes that have anti-HIV properties will aid the design of more effective therapies to treat HIV-infected patients. [unreadable] [unreadable] [unreadable]